This invention pertains to air dry, aqueous dispersed copolymer binders free of organic solvent useful in decorative and protective coatings. The binder copolymer comprises a fatty acid glyceride, typically triglycerides contained in vegetable oil, where the fatty acid chains are maleinized and then copolymerized with styrene and, optionally, other ethylenic monomers to provide a copolymer. The resulting copolymer is dispersed into water to provide a stable polymeric emulsion suitable for use as a polymeric binder for ambient dry paints.
Paint coatings are surface protective coatings applied to substrates and dried to form continuous films for decorative purposes as well as to protect the substrate. Consumer paint coatings are air-drying aqueous coatings applied primarily to architectural interior or exterior surfaces, where the coatings are sufficiently fluid to flow out, form a continuous paint film and dry at ambient temperatures to protect the substrate surface. Industrial maintenance coatings are similar coatings applied to substrates in industrial environments to primarily protect the substrate.
An aqueous based paint coating ordinarily comprises an organic polymeric binder, pigments, water, thickeners, and various paint additives. In dried paint films, the polymeric binder functions as a binder for the pigments and provides adhesion of the dried paint film to the substrate. The pigments may be organic or inorganic and functionally contribute to opacity and color in addition to durability and hardness of the dried paint film. Some paint coatings contain little or no opacifying pigments and are described as clear coatings. The manufacture of paint coatings involves the preparation of polymeric binder, mixing component materials, grinding or dispersion of pigments in a dispersant medium, and thinning to commercial standards.
The polymeric binders used in paints typically are prepared by emulsion polymerization of ethylenic monomers and are referred to as latex polymer emulsions, and the resulting paints are referred to as latex paints. Development of an emulsion polymer represents a compromise where the polymer, when formulated with pigments and fillers, must be sufficiently hard at room temperature to give reasonable mechanical and chemical resistance, while being sufficiently soft for good film formation, even at non-ideal application temperatures approaching the freezing point of water. This is conventionally accomplished by designing a latex polymer with a moderately elevated Tg (glass transition temperature) but then lowering the Tg temporarily with a volatile organic coalescing solvent. The hardness of the latex polymer must be balanced to permit drying and film formation at low application temperatures, which requires soft polymer units, while at the same time being hard enough to provide dried film resistance properties, which requires hard polymer units. This is conventionally accomplished by designing a latex polymer with a moderately elevated Tg (glass transition temperature) but then lowering the Tg temporarily with a volatile organic coalescing solvent. Coalescing solvents function to externally and temporarily plasticize the latex polymer for time sufficient to develop film formation, but then diffuse out of the coalesced film after film formation. Volatilization of the coalescent permits film formation and subsequent development of the desired film hardness, but unfortunately contributes considerably to VOC""s (volatile organic compounds) and is a significant source of residual odor, both of which are detriments in consumer air dry paints. A typical latex paint binder for instance contains copolymer consisting of major amounts of polymerized vinyl acetate, which contributes to polymer hardness, copolymerized with lesser amounts of acrylate monomer such as butyl acrylate, which contributes to polymer softening, along with volatile coalescent. Stabilization of the latex particles is accomplished through the use of anionic or nonionic surfactants which may or may not be polymerizable.
The prior art relating to copolymers of maleinized vegetable oils discloses copolymerization with various ethylenic monomer followed by emulsification of the resulting copolymer in water. U.K. patent specification No. 1,100,347 for instance discloses a water dilutable maleic modified styrenated oil for surface coatings based on utilizing a water miscible solvent for dispersing the modified oil into water, where the dispersed coating conventionally air dries with the assistance of metallic dryers. This process however produces a mixture of inadequately copolymerized components having high levels of non-copolymerized components which cannot be dispersed into water without a water miscible cosolvent, while film forming is by air drying oxidation of oils promoted by cobalt dryers to oxidize double bonds in the oil fatty acid chains. In essence, the prior art does not solve inherent compatibility problems of the multiple components copolymerized in a styrenated maleinized oil to obtain high levels of copolymerization and a resulting uniform copolymer readily dispersible into water without volatile organic cosolvents. It has been found that an insufficient level of oil copolymerized into the copolymer will generate a non-homogeneous film where free oil is incompatible with polystyrene causing phase separation, a hazy film with poor film integrity properties, and consequently an unacceptable protective coating or paint. A further inherent problem pertains to insufficient oil being copolymerized in the copolymer which in turn produces insufficient film formation flexibility and attendant film brittleness. The ability of a copolymer to form a film at ambient temperatures is dependent on achieving an acceptable range of film forming copolymer flexibility at ambient use temperatures. This generally is referred to in polymer technology as the glass transition temperature, Tg. Styrenated, maleinized oil copolymers invariably however exhibit a sharp temperature transition comparable to pure copolymer systems due to the diverse range of individual polymer structures in the copolymer. In order to obtain an acceptable air-dry decorative coatings, an acceptable range of copolymer flexibility at use temperatures must be inherent and characteristic of a copolymer. A further problem in achieving an acceptable paint product is reduction of free monomer to exceptionally low levels acceptable for a decorative coating product to avoid disagreeable odors and related health problems. Naturally occurring antioxidants present in vegetable oils, along with low reactivity of certain types of double bonds in vegetable oil, retard and inhibit free radical polymerizations making monomer conversion difficult thus leaving high final free monomer levels. Residual free monomer is an important concern in consumer paints.
It now has been found that low cost polymeric binders for air dry paints, particularly interior decorative architectural paints, including primers, can be synthesized from maleinized fatty acid glycerides, such as triglycerides in vegetable oils, and overpolymerized with styrene in the absence of organic solvent to produce a copolymer binder. The copolymer can be treated with amine or ammonium hydroxide to produce a carboxyl functional copolymer which can be dispersed into water to form an aqueous dispersed copolymer particularly useful for air dry paint coatings without the need for metallic dryers. The dried paint films are clear films which exhibit good hardness and flexibility, good water resistance, along with good wet adhesion properties. The copolymer binder substantially reduces or essentially eliminates conventional hydroxyethylcellulose thickeners, an expensive thickener material, while preferred low cost acrylic thickeners are particularly effective with the copolymers of this invention. The copolymers of this invention can be processed without volatile organic solvents while the paint coatings produced are essentially VOC free. Close to 50% by weight of the copolymer comprises renewable vegetable oils as opposed to non-renewable petrochemicals.
In accordance with this invention, sufficient copolymerization of the oil into the copolymer can be achieved to yield a clear, dried resilient film indicating the various components are sufficiently copolymerized. An important aspect of this invention is to considerably increase the level of fatty acid glyceride oil copolymerized into the resulting copolymer to produce a polymeric film which remains clear and avoids phase separation over time. The copolymer is sufficiently plasticized by oil copolymerized into the copolymer to be capable of low temperature film formation. Copolymer binders can be produced for decorative coatings without the use of coalescent solvents, a primary contributor to VOC level. The copolymer binder becomes film forming when applied at or above 40xc2x0 F. without the need for coalescing solvent. By the appropriate selection of initiator type and amount, very low free monomer levels required for decorative coatings can be obtained. An other unanticipated advantage of this invention is the excellent thickener response of the paint formulated due to the low quantities of thickener required to achieve desired paint viscosity. An additional advantage is that low volume solids paints, relative to conventional paints, can be formulated at desired paint viscosity with conventional levels of various paint thickeners. Conventional metallic dryers such as cobalt naphthenate are not required nor desired. These and other advantages of this invention will become more apparent by referring to the detailed description and the illustrative examples.
Briefly, the invention pertains to ambient dry paints containing a copolymer binder based on maleinized non-conjugated unsaturated fatty acid glycerides overpolymerized with styrene in absence of volatile organic solvent to produce a copolymer followed by dispersion of the copolymer into water to form a water dispersed copolymer. Preferred glycerides are triglycerides. The maleinized fatty acid triglyceride is formed by reacting maleic anhydride at high temperatures to preferentially form a maleic anhydride structure pendently attached to the fatty acid chain on the triglyceride. The maleinized fatty acid triglycerides are copolymerized with styrene along with a minor amount of other ethylenic monomers, if desired, in the presence of free radical initiators and in the absence of solvents and water. The resulting copolymer is a styrenated malenized fatty acid triglyceride copolymer. The copolymer is reacted with water or alcohol to open the anhydride and form carboxyl groups which can be neutralized with amine or ammonium hydroxide, and then dispersed into water. The copolymer preferably comprises by weight 40% to 50% copolymerized fatty acid triglyceride, 40% to 55% copolymerized monomer including styrene, with the balance being 3% to 12% copolymerized maleic anhydride. The most preferred composition comprises between 42% and 48% copolymerized fatty acid triglyceride oil, between 42% and 52% copolymerized styrene and other ethylenic monomers, with the balance being 6% to 10% copolymerized maleic anhydride.
In accordance with the process of this invention, non-conjugated unsaturated fatty acid glyceride oil is first maleinized at high temperatures to form a maleinized fatty acid glyceride, which is then overpolymerized with styrene and lesser minor amounts of other ethylenic monomers if desired. The styrene polymerization step is at high temperatures and high initiator levels, in absence of water and volatile organic solvents, to form a styrenated maleinized modified fatty acid glyceride copolymer. The copolymer is reacted with water or alcohol to open the anhydride and form carboxyl functionality. The resulting carboxyl functional copolymer can be dispersed into water with amine neutralization of the carboxyl groups to form a water dispersed copolymer suitable for use as polymeric binder for aqueous dispersed air dry paints.